Process for preparing amorphous, catalytically active silicoaluminas

Info

Patent number: 5888466
Type: Grant
Filed: Oct 21, 1996
Date of Patent: Mar 30, 1999
Assignees: Eniricerche S.p.A. (Milan), Agip Petroli S.p.A. (Rome), Enichem Synthesis S.p.A. (Palermo)
Inventors: Carlo Perego (Milan), Stefano Peratello (Milan), Roberto Millini (Milan)
Primary Examiner: Michael Lewis
Assistant Examiner: Stuart L. Hendrickson
Law Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Application Number: 8/734,683

Abstract

An amorphous, micro/mesoporous silica-alumina gel with controlled pore size, having a surface area of at least 500 m.sup.2 /g and with a molar ratio of SiO.sub.2 :Al.sub.2 O.sub.3 of at least 30:1, is prepared by hydrolysing and causing a tetra-alkyl ammonium hydroxide, an aluminum trialkoxide, and a tetra-alkyl orthosilicate to gelate, by operating at a temperature equal to, or higher than, the boiling temperature, under atmospheric pressure, of any alcohols which are developed as a by-product from said hydrolysis reaction, without said alcohols being removed, or being substantially removed, from the reaction media; and the so produced gel being dried and fired.

Claims

1. A process for preparing an amorphous micro-mesoporous silica-alumina gel having a surface area of at least 500 m.sup.2 /g and a pore volume of 0.4-0.8 cm.sup.3 /g with a molar ratio of SiO.sub.2:Al.sub.2 O.sub.3 of at least 30:1, comprising the steps of:

(1) hydrolyzing and gelling an reaction medium comprising a tetra-(C.sub.2 -C.sub.5)-alkyl ammonium hydroxide, an aluminum tri-(C.sub.2 -C.sub.4)-alkoxide and a tetra-(C.sub.1 -C.sub.5)-alkyl orthosilicate at a temperature equal to or higher than the boiling temperature at atmospheric pressure of any alcohol produced during said hydrolyzing and gelling steps, in a closed system without substantially removing said alcohol from said reaction media to produce a gel; and

(2) drying and firing said gel, and (3) recovering said gel.

2. The process of claim 1, wherein said tetra-(C.sub.2 -C.sub.5)-alkyl ammonium hydroxide is selected from the group consisting of tetrapropyl ammonium hydroxide, tetraisopropyl ammonium hydroxide and tetrabutyl ammonium hydroxide, said aluminum tri-(C.sub.2 -C.sub.4)-alkoxide is selected from the group consisting of aluminum tripropoxide and aluminum triisopropoxide, and said tetra-(C.sub.1 -C.sub.4)-alkyl orthosilicate is tetraethyl orthosilicate.

3. The process of claim 1, further comprising prior to said hydrolyzing step,

preparing an aqueous solution containing said tetra-(C.sub.2 -C.sub.5)-alkyl ammonium hydroxide and said aluminum tri-(C.sub.2 -C.sub.4)-alkoxide and adding said tetra-(C.sub.1 -C.sub.5)-alkyl orthosilicate to said solution at a temperature lower than the temperature of said hydrolyzing, wherein the molar ratio SiO.sub.2:Al.sub.1 O.sub.3 is 30:1 to 500:1, the molar ratio tetra-(C.sub.2 -C.sub.5)-alkyl ammonium hydroxide:SiO.sub.2 is 0.05:1 to 0.2:1 and the molar ratio H.sub.2 O:SiO.sub.2 is 5:1 to 40:1.

4. The process of claim 3, wherein said hydrolyzing and gelling is conducted at a temperature of about 65.degree. C. up to about 110.degree. C.

5. The process of claim 1, wherein said reaction medium contains an alcohol in an amount up to a maximum molar ratio alcohol:SiO.sub.2 of 8:1.

6. The process of claim 5, wherein said alcohol is ethanol.

7. The process of claim 1, wherein said hydrolyzing and gelling is conducted for a time ranging from 10 minutes to 3 hours.

8. The process of claim 7, wherein said hydrolyzing and gelling is conducted for a time ranging from 1-2 hours.

9. The process of claim 1, further comprising aging said gel at room temperature for 1-24 hours between steps (1) and (2).

10. The process of claim 1, further comprising removing said alcohol produced during said hydrolyzing and gelling step from said gel and then vacuum drying said gel to produce a dried gel, and firing said dried gel in an oxidizing atmosphere at a temperature in the range from 500.degree. to 700.degree. C. for a time ranging from 4 to 20 hours.

11. The process of claim 10, wherein said firing is at a temperature of 500.degree.-600.degree. C. for a time ranging from 6-10 hours.

12. A process for preparing an amorphous silica-alumina gel having a surface area of at least 500 m.sup.2 /g and a pore volume of 0.4-0.8 cm.sup.3 /g with a molar ratio of SiO.sub.2:Al1.sub.2 O.sub.3 of at least 30:1, comprising the steps of:

(1) hydrolyzing and gelling an aqueous reaction medium comprising a tetra-(C.sub.2 -C.sub.5)-alkyl ammonium hydroxide, an aluminum tri-(C.sub.2 -C.sub.4)-alkoxide and a tetra-(C.sub.1 -C.sub.5)-alkyl orthosilicate at a temperature equal to or higher than the boiling temperature at atmospheric pressure of any alcohol produced during said hydrolyzing and gelling steps, in a closed system without substantially removing said alcohol from said reaction media to produce a gel;

(2) drying and firing said gel, and (3) recovering said gel

wherein said hydrolyzing gelling are conducted at a temperature of 82.degree. C. to about 110.degree. C.

13. The process of claim 12, wherein said hydrolyzing and gelling is conducted at a temperature of 88.degree. C. to about 110.degree. C.

14. The process of claim 1, wherein said dried and fired gel has an average pore radius from 10 to about 20.ANG..

15. The process of claim 1, wherein said dried and fired gel has a surface area of from 600-850 m.sup.2 /g.

16. The process of claim 1, wherein hydrolyzing and gelling is conducted in an autoclave under the autogenous system temperature, or under atmospheric pressure inside a reactor equipped with a reflux condenser.